Action Surge is a Fighter feature gained at level 2 in the 2024 SRD. You can push yourself beyond your normal limits for a moment.
You can push yourself beyond your normal limits for a moment. On your turn, you can take one additional action, except the Magic action.
Once you use this feature, you can't do so again until you finish a Short or Long Rest. Starting at level 17, you can use it twice before a rest but only once on a turn.